Difference between GC and HPLC Techniques

Gas Chromatography and the High Performance Liquid Chromatography system are separation techniques used in obtaining specific eluents from an analyte basing on the compounds in the analyte distribution between the two phases (Mobile phase and Stationary phase). The mobile phase is the part in chromatography which moves and it usually contains the sample while the stationary phase is one which does not move and contains adsorption material. Chromatography is a larger analytical technique in chemistry.

In modern-day analytical chemistry, Gas Chromatography and the High Performance Liquid Chromatography system are the major techniques used in Analytical Chemistry. In an earlier analysis technique such as the Ion Exchange Chromatography, Affinity Chromatography and Thin Layer Chromatography were used. Both these techniques are effective for separation of the analytes. The difference between the two techniques are discussed in different subtopics below:

1. Mobile Phase: One of the major differences between these two methods is the difference in their mobile phases which eventually determines where each technique is used.

As the name suggests, gas chromatography uses gases as its mobile phase with the stationary phase either be liquid or solid. On the other hand, High Performance Liquid Chromatography system uses a liquid as its mobile phase and a solid as its stationary phase in the analysis.

2. Nature of Analyte: Compared to High Performance Liquid Chromatography, Gas Chromatography analyzes samples that are either volatile or semi-volatile thus it will analyze only a few samples since volatile compounds are fewer than non-volatile samples which the HPLC analyzes. Inadvertently, HPLC analyzes samples that are only liquid in nature.

3. Instrumentation: Both these methods use chromatography columns, but there is differentiation in their sizes. The gas chromatography uses columns which are long and thick usually 10 to 30 meters in length as compared to the chromatography column which is shorter and thin basically being 5 to 25 cm in length.

4. Detection: After chromatography is done on the analyte, the composition of the eluent has to be done. This calls for detection methods that are stringent to get the perfect sample type and volume. Each analytical technique has its own method of sample detection. For gas chromatography, two types of detectors are the most widely used i.e the Flame Ionization Detector (FID) that is only used for detection of hydrocarbons and the Thermal Conducting Detector (TCD) which is universal and detects any substance.

In the case of High Performance Liquid Chromatography system, the only method use is via an Ultraviolet Spectrometric detector which uses the principle of absorption and transmittance to detect the different types of samples In spectrophotometry, a sample is placed between a source of light and a photometric reader. The amount of light passing through the sample is recorded as photons by a computer detector. Different samples have different absorbance rates.

5. Cost: Finally, the cost of each technique is a determining factor. The Gas Chromatography technique is less costly compared to the HPLC system that utilizes a lot of equipment including high pressure pumps to increase its accuracy and shorten the time required for analysis of the sample. This makes Gas Chromatography being used more compared to HPLC.